The present invention relates to a nonwoven fabric having at least two layers of nonwoven web. More particularly, the present invention relates to a nonwoven fabric wherein at least one of the layers comprises a web having monofilaments or fibers with a bilobal cross-section as well as methods for making such multilayered nonwoven fabrics.
Nonwoven materials are, of course, well known in the art. Such materials were developed primarily in the 1950's and 1960's, although at least one reference dates back to 1943 (see, e.g., U.S. Pat. No. 2,336,743 to Manning).
One of the most significant commercial applications of nonwoven fabrics is in the fabrication of disposable products intended for a single use. Typical of such products are disposable diapers, feminine care products, surgical gowns, industrial wipes, and the like. Because the nonwoven fabric is intended as a cloth substitute in these applications, extensive effort has been expended to improve the properties of nonwoven fabric to more nearly approximate that of cloth. Of particular interest has been the softness of the nonwoven fabric, that is, improving the feel or "hand" of the fabric together with lowering the resistance of the web to folding or bending. Another important area has been the improvement of the nonwoven web's tensile strength or tear resistance. Yet another areas has been the development of nonwoven fabrics with specific wettability characteristics. With the few exceptions noted below, these efforts to improve the properties of nonwoven webs has focused almost exclusively on the use of fibers having a circular cross-section.
U S. Pat. No. 2,336,743 to Manning describes a method and apparatus for solution spinning or melt spinning nonwoven fabrics. According to the specification, the spinning material can be extruded through orifices in the spinneret, which orifices may be slits, circular, or of other cross-section.
U.S. Pat. No. 3,314,840 to Lloyd et al. relates to a process and apparatus for producing a nonwoven fabric. Although the disclosure appears to relate primarily to solution spinning, it does not appear to exclude melt spinning. The spinneret preferably has circular or slit openings, although such openings may have other shapes such as circles, triangles, crescents, etc.
U S. Pat. No. 3,508,390 to Bagnall et al. relates to a modified filament and fabrics produced therefrom. While the emphasis of the disclosure is on the preparation of conventional knitted fabrics, nonwoven fabrics are also mentioned. The filament has a cross-section consisting of three integrally joined, substantially symmetrical legs, thereby forming a substantially uniform Y-shaped cross-section having defined dimensions.
U.S. Pat. No. 3,509,009 to Hartmann relates to a nonwoven fabric which is prepared by meltspinning fiber-forming high polymers into a directed gass current of high velocity to produce a uniform nonwoven fabric of great strength. While the filaments produced in accordance with the described invention are typically of circular cross-section, other cross-sections are mentioned, such as star-shaped, Y-shaped, or a combination thereof.
An apparatus for producing nonwoven fleeces is described in U.S. Pat. No. 3,528,129 also to Hartmann. The patent appears to be an improvement of an existing apparatus by specifying holes in the spinneret which have a branched cross-section. Y-shaped and T-shaped holes are specifically mentioned.
Finally, U.S. Pat. No. 3,630,816 to Parker relates to nonwoven sheets made from filaments having a rectangular cross-section. The rectangular cross-section of these filaments is specficed to have an aspect ratio of at least 3:1.